A semiconductor device has a plurality of layers on a silicon substrate. The layers are deposited on the substrate through a deposition process. The deposition process has several important issues, which are important in evaluating deposited films and selecting a deposition method.
One of the important issues is quality of the deposited films. The quality includes composition, contamination level, defect density, and mechanical and electrical properties. The composition of films may change depending upon deposition conditions, which is very important in obtaining a specific composition.
Another important issue is uniform thickness over a wafer. In particular, the thickness of a film deposited at the top of a nonplanar pattern having a step is very important. Whether the thickness of the deposited film is uniform or not may be determined by a step coverage defined as a value obtained by dividing the minimum thickness of the film deposited at the step part by the thickness of the film deposited at the top of the pattern.
Another issue related to the deposition is space filling, which includes gap filling to fill gaps defined between metal lines with an insulation film including an oxide film. The gaps are provided to physically and electrically insulate the metal lines.
Among the above-described issues, the uniformity is one of the important issues related to the deposition process. A nonuniform film causes high electrical resistance on the metal lines, which increases a possibility of mechanical breakage.